1. Field of the Invention
The invention relates to tracking systems, particularly to such systems that determine position and orientation of an object in a limited volume using accelerometers.
2. Description of the Background Art
In specialized computer applications involving virtual reality or "immersive simulations" a computer or processing facility providing the simulation must continuously determine with a high degree of accuracy the position and orientation of a user (or part of the user e.g., head or hand) relative to a "virtual world" or simulated environment in which the user operates. The position and orientation data must be updated regularly to provide a realistic simulation. In addition, the data must be collected in a manner that does not interfere significantly with the user's natural movement. Thus, physical connection to a stationary object or heavy and/or bulky tracking instruments attached to the user are unsuitable. In order to be integrated easily with a head-mounted display (HMD), data glove or other peripheral device for use in a virtual reality application, a tracking system must be small and light weight.
A mechanical gantry containing sensors is used to track movement by physically connecting the user to a fixed object. However, this system is cumbersome, provides an unrealistic simulation due to interferences from the gantry, and requires significant installation effort.
A simplified radar or sonar system having a transmitter and a receiver mounted on the user is used to determine position of an object. However, this type of system is sensitive to noise in the environment, tends to have high frequency jitter between position measurements, is subject to interference from other objects in the simulation (e.g., a hand or other users), is generally bulky, requires multiple transmitters and receivers, and may be quite complex and expensive. Such systems are embodied in products available commercially from Polhemus, Logitech, and Ascension Technology.
Additionally, conventional navigation systems for navigating over large areas of land or airspace such as those for planes, cars, missiles, use devices such as gyroscopes that are not suitable for attachment to a human user because of their size and weight. In addition, these devices are typically designed to track over several hundred kilometers and several days, and are accurate only to several meters.
Two-dimensional navigation systems using angular accelerometers (a type of gyroscope), such as that used in Barber U.S. Pat. No. 5,245,537, are not suitable for virtual reality applications requiring three position and three orientation measurements for realistic simulation. The system described in Barber does not provide a highly accurate measurement (as required by virtual reality applications) because it contains no mechanism for correcting errors that are inherent in the system (e.g., bias, calibration errors, floating, and positional errors). Left uncorrected, these errors typically increase in size as a function of time of use and/or volume traversed, thereby resulting in a significant degradation in system performance. Moreover, angular accelerometers are not easily integrated into electronic componentry, thus the resulting system is generally greater in size and weight and is not suitable for attachment to a human user. In addition, a much higher update rate (e.g., 50-300 Hz) than that used in Barber is required for realistic virtual reality simulations.
Thus, there is a need for a small, lightweight, highly integratable, navigational system that can be easily attached to a human user without significant interference to natural body movement. Furthermore, there is a need for a navigational system that is highly accurate over a long period of time and operates at a high update rate in order to provide a realistic virtual reality simulation. The prior art has failed to address these needs adequately.